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#95726 - 10/01/05 07:22 PM voltage irregularity on 240v
Tripp Offline
Member
Registered: 09/20/05
Posts: 99
Some time back I had some folks who needed me to take a subfeed from a subpanel. That is to say, they had a 2-pole 50a breaker at the main house panel feeding a subpanel in the shop. From this subpanel they wanted me to take a 2-pole 30a to a second subpanel. The problem was that when I checked voltage at the subpanel in the shop, I found 120v on one phase to neutral but only ~46v to neutral on the second phase, giving me phase-to-phase voltage of ~166v. The best I could determine (i.e., guess) at the time was that one of the phases was grounded somewhere in the underground run between house and shop - only just not enough of a ground to trip a breaker.

Does anyone out there have any other ideas of what the problem could have been?
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#95727 - 10/01/05 07:26 PM Re: voltage irregularity on 240v
gfretwell Offline


Member
Registered: 07/20/04
Posts: 9038
Loc: Estero,Fl,usa
Sounds more like a bad connection or a gopher bit wire.
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Greg Fretwell
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#95728 - 10/02/05 05:08 AM Re: voltage irregularity on 240v
iwire Offline
Moderator
Registered: 01/05/03
Posts: 4391
Loc: North Attleboro, MA USA
You used a digital multi meter to test I bet?

Take a couple of minutes to read this thread about Phantom voltage and DMMs then come back here.
http://electrical-contractor.net/ubb/Forum1/HTML/006361.html

Open all the breakers in the sub panel, then use a old fashioned wiggy to test from each hot to ground.

I bet you will find that the wire that showed 46 volts is actually dead.

If one of the phases was grounded enough to lose about 80 volts the breaker would trip.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts
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#95729 - 10/02/05 12:21 PM Re: voltage irregularity on 240v
Tripp Offline
Member
Registered: 09/20/05
Posts: 99
Thanks, Bob. I've read some of the phantom voltage posts on this forum before, but didn't think to apply the concept here. I will try what you suggested with my wiggy.

In the meantime, if i assume the phase is dead, i think i'm in the same boat either way. Don't know what caused the "death", but know i have to pull a new feed. Yes?
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#95730 - 10/02/05 12:26 PM Re: voltage irregularity on 240v
GalwayElectric Offline
Member
Registered: 09/22/05
Posts: 14
Loc: Rutherford, NJ
I would agree Tripp unless the feeds not the problem. What about the breaker on the feed end? The 50 amp one. Maybe half of that is bad or the connection is lose? Or even the terminal in the panel that feeds that 50 amp. Maybe the prong has broken off there? (Although I doubt it). Alot of times the wire where it is connected to a breaker or lug or whatever when it was installed they scored the wire too hard and after time with heat and vibration has come lose. And you can even see it with your naked eye unless you stick your hand in there and try to move the wire and the whole thing comes right off in your hand.

In my opinion before you pull a new feed check for a list of these things and more before you go to the trouble and expense of pulling in a whole new feed.

Good luck.
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#95731 - 10/02/05 01:01 PM Re: voltage irregularity on 240v
Tripp Offline
Member
Registered: 09/20/05
Posts: 99
Thanks, Galway. I remember I did a DMM check at the original panel in the house where the 2-pole 50a is, and the reading was fine. Is there any other way to check if the problem is there at the source?
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#95732 - 10/02/05 03:05 PM Re: voltage irregularity on 240v
renosteinke Offline
Cat Servant
Member
Registered: 01/22/05
Posts: 5316
Loc: Blue Collar Country
Open neutral/ degraded neutral connection anyone?
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#95733 - 10/02/05 03:13 PM Re: voltage irregularity on 240v
iwire Offline
Moderator
Registered: 01/05/03
Posts: 4391
Loc: North Attleboro, MA USA
It certainly could be, it depends if his measurements where really hot to neutral or hot to ground.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts
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#95734 - 10/02/05 03:27 PM Re: voltage irregularity on 240v
iwire Offline
Moderator
Registered: 01/05/03
Posts: 4391
Loc: North Attleboro, MA USA
Never mind I take that back, it can not be a neutral problem.

The voltage is correct on one leg and off on the other leg.

A bad neutral would show up on both legs, one would be high and the other low.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts
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#95735 - 10/02/05 07:22 PM Re: voltage irregularity on 240v
Tripp Offline
Member
Registered: 09/20/05
Posts: 99
You beat me to it, Bob: if the reading was 120v on one phase to neutral, then neutral's not the prob.
But for what it's worth, my DMM measurements were Hot to Neutral and Hot to Hot. As a matter of fact, there was no Ground pulled in the original subfeed - something i plan on remedying when i pull my new subfeed. But first i must get back out there with my wiggy.
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